Summary: Eye movements distinguish between “go” and “no go” actions early in the decision-making process, before the hand even starts to move.
Source: American Physiological Society
New research suggests that eye movements may come before hand movements in actions that require a two-step decision-making process. The study is published ahead of print in the Journal of Neurophysiology (JNP).
Most people are faced with real-life opportunities to make choices that involve both senses and motor skills every day. For example, when a squirrel runs across the street, a driver must decide to avoid hitting it. This sequence of events involves first making the decision to brake the car and then putting the motor skills to work to execute the action. Visually guided decision-making in movement tasks—how the eyes and the body work together—is a research area that is lacking.
A research team from the University of British Columbia in Canada explored whether eye movements are the consequence of decision-making, coming after the decision is made, or if they reflect making a choice and occur before the decision is made.
Young adult volunteers with an average age of 19 participated in a tracking activity in which an animated ball moved across a computer screen. The ball was randomly programmed to either pass through or miss a strike box on the screen. The volunteers were instructed to track the ball with their eyes, decide whether the ball would pass or miss the box and intercept a pass by touching the screen with the index finger of their dominant hand (“go” action). If the volunteers thought the ball would miss the box, they did not touch the screen (“no-go” action). The ball was launched from several different angles and appeared on the screen for very brief periods of time, ranging from 100 to 300 milliseconds.
The researchers measured the volunteers’ eye position signals—including speed and acceleration of eye movements—with a video tracking system. Sensors attached to the dominant index finger recorded finger position throughout the trial. Eye tracking captured both “smooth pursuit” movements—where the eyes closely follow a moving object—and the quicker, jerky motions associated with activities such as reading, called saccades. The researchers also analyzed the interception decision accuracy of the volunteers’ “go” and “no-go” actions (whether or not to move their hand).
The research team found that “eye movements distinguished go/no-go actions early in the decision process, before the hand first started to move.” Smooth pursuit movements in particular corresponded with the accuracy of the decision to intercept the ball or not and the timing of when to begin the interception. “This finding emphasizes that eye movements may indicate go/no-go actions before hand movements are executed,” the researchers wrote. “Because eye movements occur naturally and spontaneously, this may open new avenues for studying decision-making processes in real-world scenarios.”
About this neuroscience research article
Source: American Physiological Society Media Contacts: APS Communications Office – American Physiological Society Image Source: The image is in the public domain.
Eye movements as a readout of sensorimotor decision processes
Real-world tasks, such as avoiding obstacles, require a sequence of interdependent choices to reach accurate motor actions. Yet, most studies on primate decision making involve simple one-step choices. Here we analyse motor actions to investigate how sensorimotor decisions develop over time. In a go/no-go interception task human observers (n=42) judged whether a briefly-presented moving target would pass (interceptive hand movement required) or miss (no hand movement required) a strike box while their eye and hand movements were recorded. Go/no-go decision formation had to occur within the first few hundred milliseconds to allow time-critical interception. We found that the earliest time point at which eye movements started to differentiate actions (go vs. no-go) preceded hand movement onset. Moreover, eye movements were related to different stages of decision making. Whereas higher eye velocity during smooth pursuit initiation was related to more accurate interception decisions (whether or not to act), faster pursuit maintenance was associated with more accurate timing decisions (when to act). These results indicate that pursuit initiation and maintenance are continuously linked to ongoing sensorimotor decision formation.